Substance abusing and dependent delinquents represent a greatly under served population that is at high risk of deleterious long-term outcomes and costs (emotional, physical, financial) for themselves, their families, communities, and society. The proposed follow-up (competing continuation) to an ongoing randomized clinical trial provides a unique opportunity to examine the capacity of an evidence-based treatment (i.e., multisystemic therapy, MST; Henggeler, Schoenwald, Borduin, Rowland, & Cunningham, 1998) to attenuate such deleterious long-term (5-years post recruitment) outcomes and costs in a sample of 200. This randomized trial includes four treatment conditions (Community Services vs. Drug Court with Community Services vs. Drug Court with MST vs. Drug Court with MST enhanced with contingency management), two of which were originally funded by NIAAA (AA122202) and two of which were added through NIDA funding (i.e., DA13066). The current follow-up is 18 months post recruitment, and the proposed study extends the follow-up to 5 years post recruitment, with assessments conducted at 2, 3, 4, and 5 years post recruitment. The extended follow-up would address several important gaps in the adolescent substance abuse treatment literature including (a) lack of long-term follow-up to randomized trials, (b) lack of research on the clinical effectiveness and economic aspects of treatments of adolescent substance abusers; (c) lack of research on mediators of decreased adolescent substance use; and (d) lack of research on individual and contextual moderating variables. Specific aims, therefore, include: Aim 1. Evaluate long-term treatment effects on adolescent and young adult alcohol and drug use, criminal activity, and mental health functioning; as well as on family relations, peer relations, and school attendance employment. Aim 2. Track adolescent substance abuse and mental health service utilization, juvenile justice involvement, and out-of-home placements (e.g., foster placement, incarceration, placement in residential treatment center, inpatient treatment) and their associated costs across the treatment conditions for 5 years post recruitment. Aim 3. Test hypotheses about the mediators and moderators of MST treatment effects.